Currently, photonic integrated circuits allow the integration of practically all active or passive optical devices, such as, for example, coupling structures, waveguides, modulators, or photodetectors.
Moreover, another known advantageous component is a hybrid III-V/Si laser source. Such a laser source includes an amplifying medium (gain medium) that includes a composite III-V semiconductor material, a waveguide situated in an underlying silicon layer and optically coupled to the gain medium, and a cavity resonator optically coupled to the waveguide and containing Bragg mirrors, for example. The gain medium emits light when it is excited by electrical energy (pumping), and the cavity resonator is intended, in cooperation with the gain medium, to amplify this light so as to deliver the laser beam.
Depending on the type of laser (DBR: Distributed Bragg Reflector or DFB: Distributed Feedback laser), the Bragg mirrors are situated in the silicon at the periphery of the gain medium or else under the gain medium.
Such a hybrid laser source may require a very short distance, typically not more than a hundred nanometers, between the gain medium and the underlying silicon waveguide. Moreover, direct bonding of the gain medium to a waveguide of silicon-on-insulator type typically requires a planar surface prepared by a chemical-mechanical polishing step. Currently, a hybrid III-V laser source on a silicon substrate can be manufactured on an experimental basis and in isolation.
Integrated photonic circuits generally do not incorporate hybrid III-V/Si laser sources due to the great difficulty of integrating these sources. This is because direct bonding to the silicon-on-insulator film cannot be carried out after the complete production of the integrated circuit, and particularly after the production of the metallization levels of the interconnect part of the integrated circuit, widely denoted as the Back End Of Line (BEOL) part by those skilled in the art.
Furthermore, conventional production of the metallization levels (using deposition and chemical-mechanical polishing (CMP) of dielectrics/metals) cannot be carried out after any steps of integration of the laser source due to the substantial height of the laser source, typically about 3 microns. As a result hybrid III-V laser sources may therefore be incompatible with integration into integrated circuits. Therefore, the approach currently used to associate a laser source with an integrated circuit includes, after the integrated circuit and its interconnect (BEOL) part have been produced, fixing an already assembled laser source to one of the sides of the chip.